Just checked Nintendo's netcode (first heard about this word) while waiting for splatoon 3 to unlock.

https://oatmealdome.me/blog/splatoon-2s-netcode-an-in-depth-look/

https://oatmealdome.me/blog/an-in-depth-look-at-the-splatoon-2-ranking-system/

And some people said they would use a new system called NPLN, but I didn't find too much info about that.

It's amazing to see the player community can do such a great reverse engineering, while Nintendo didn't reveal anything (despite some accidental debug info leak).